1. Field of the Invention
The present invention relates to a magnetoresistive head which reads information written onto a magnetic recording medium, and more specifically to a magnetoresistive head of a novel longitudinal biasing method of a ferromagnetic layer for detecting a signal field and the fabricating method.
2. Description of the Related Art
In a magnetoresistive head mounted as a reading element on a magnetic recording and reading device, a GMR (Giant Magnetoresistive) head using a spin valve film having a basic structure of ferromagnetic free layer/nonmagnetic conductive layer/ferromagnetic film fixing layer/antiferromagnetic layer described in Japanese Published Unexamined Patent Application No. Hei 4-358310 is widely used at present. In the magnetoresistive head, in order to inhibit Barkhausen noise, longitudinal biasing must be performed to a ferromagnetic free layer whose magnetization direction is changed by a signal field. As the longitudinal biasing method, Japanese Published Unexamined Patent Application No. Hei 7-57223 describes a method in which a hard magnetic film or a deposited film of a ferromagnetic film and an antiferromagnetic film is arranged at each edge of a magnetoresistive film to set a ferromagnetic free layer on single domain state. The former is called a hard biasing structure which is the mainstream of the current head structure.
The hard biasing structure applies a longitudinal biasing field to a ferromagnetic free layer and is effective for inhibiting Barkhausen noise. On the other hand, it is widely known that magnetization at the edge of an element is fixed to form the so-called insensitive zone. Since the magnetization direction in the insensitive zone is not changed by a signal field, formation of the insensitive zone substantially reduces the reading sensitivity. With the future increase of the surface recording density of a magnetic recording and reading device, the track width is being reduced to increase the occupying percentage of the insensitive zone. This problem is expected to be significant.
To reduce formation of the insensitive zone for the purpose of ensuring the reading sensitivity, the film thickness of a hard magnetic film is decreased to reduce a longitudinal biasing field applied to the ferromagnetic free layer. The effect for inhibiting Barkhausen noise is insufficient. This means that inhibition of Barkhausen noise and reduction of insensitive zone formation are in a trade-off relation
As another means for performing longitudinal biasing to a ferromagnetic free layer, Japanese Published Unexamined Patent Application No. 2000-173020 describes a longitudinal biasing structure by interface exchange coupling. Since this structure exchange couples the entire surface of a ferromagnetic free layer to an antiferromagnetic layer, it has a reliable and uniform longitudinal biasing effect. In the hard biasing structure previously described, the geometrical arrangement relation between a hard magnetic film and a ferromagnetic free layer and the shape of an element by patterning affect the magnitude of the longitudinal biasing field. On the contrary, in the longitudinal biasing structure by interface exchange coupling, antiferromagnetic material and its film thickness are selected and a suitable exchange coupling field biasing layer is interposed between a ferromagnetic free layer and an antiferromagnetic layer. An advantage of easily adjusting a longitudinal biasing field can be expected. Since a magnetic pole is caused at the edge of the ferromagnetic free layer, magnetization of the edge is expected to be unstable. A sufficient longitudinal biasing effect cannot be obtained. The influence of this is expected to be significant as the geometrical track width is being reduced.
In consideration of the future increase of the surface recording density of a magnetic recording and reading device, as described above, it can be expected that it is difficult to realize both inhibition of Barkhausen noise and ensuring of the reading sensitivity in the hard biasing structure, and reduction of the reading track width in the longitudinal biasing structure by interface exchange coupling. The prior art longitudinal biasing means cannot obtain reading characteristic which can correspond to the future magnetic recording and reading device with a high recording density and imposes an important problem of establishment of novel longitudinal biasing means. This is not limited to the current CIP (Current in the plane)xe2x80x94GMR head, but is a common problem for a CPP (Current perpendicular to the plane)xe2x80x94GMR head and a TMR (Tunneling Magnetoresistive) head which are expected to be practical as the next generation head.
Accordingly, an object of the present invention is to provide a magnetoresistive head which applies longitudinal biasing means satisfying all of inhibition of Barkhausen noise, high reading sensitivity, and reduction of an effective reading track width and the fabricating method.
To achieve the foregoing object, in the present invention, a magnetoresistive head having a first and a second ferromagnetic layers separated by a nonmagnetic conductive layer or a nonmagnetic tunneling barrier layer; a magnetoresistive film in which the magnetization direction of the first ferromagnetic layer is fixed by a first antiferromagnetic layer provided to be contacted with the first ferromagnetic layer opposite to the nonmagnetic conductive layer or the nonmagnetic tunneling barrier layer; and a pair of electrodes for flowing a sense current to the magnetoresistive film, includes: a second antiferromagnetic layer arranged so as to provide unidirectional magnetic anisotropy to the second ferromagnetic layer; and a hard magnetic film arranged so as to apply a magnetic field to the second ferromagnetic layer.
In the present invention, a second antiferromagnetic layer is formed to be contacted with the second ferromagnetic layer opposite to the nonmagnetic conductive layer or the nonmagnetic tunneling barrier layer, and a hard magnetic film is formed at each edge of the magnetoresistive film in the track width direction.
In the present invention, a magnetoresistive head having a first and a second ferromagnetic layers separated by a nonmagnetic conductive layer or a nonmagnetic tunneling barrier layer; a magnetoresistive film in which the magnetization direction of the first ferromagnetic layer is fixed by a first antiferromagnetic layer provided to be contacted with the first ferromagnetic layer opposite to the nonmagnetic conductive layer or the nonmagnetic tunneling barrier layer; a magnetic flux guide for guiding an external magnetic field to the second ferromagnetic layer; and a pair of electrodes for flowing a sense current to the magnetoresistive film, includes: a second antiferromagnetic layer arranged so as to provide unidirectional magnetic anisotropy to the second ferromagnetic layer; a third antiferromagnetic layer arranged so as to provide unidirectional magnetic anisotropy to the magnetic flux guide; and a hard magnetic film arranged so as to apply a magnetic field to the second ferromagnetic layer and the magnetic flux guide.
A second antiferromagnetic layer is formed to be contacted with the second ferromagnetic layer opposite to the nonmagnetic conductive layer or the nonmagnetic tunneling barrier layer, a third antiferromagnetic layer is formed to be contacted with the magnetic flux guide, and a hard magnetic film is formed at each edge of the magnetoresistive film in the track width direction and at each edge of the magnetic flux guide in the track width direction.
The direction of unidirectional magnetic anisotropy provided to the second ferromagnetic layer by the second antiferromagnetic layer or the direction of unidirectional magnetic anisotropy provided to the magnetic flux guide by the third antiferromagnetic layer, and the direction of a magnetic field applied to the second ferromagnetic layer or the magnetic flux guide from the hard magnetic film are roughly matched.
The direction of unidirectional magnetic anisotropy provided to the first ferromagnetic layer by the first antiferromagnetic layer and the direction of unidirectional magnetic anisotropy provided to the second ferromagnetic layer by the second antiferromagnetic layer or the direction of unidirectional magnetic anisotropy provided to the magnetic flux guide by the third antiferromagnetic layer are roughly orthogonal, and when temperatures at which unidirectional magnetic anisotropy disappears (blocking temperatures) in the first antiferromagnetic layer, the second antiferromagnetic layer and the third antiferromagnetic layer are TB1, TB2 and TB3, TBB1 greater than TB2=TB3.
When a saturation flux density of the second ferromagnetic layer is BS2, its film thickness is t2, a remaining flux density of the hard magnetic film is Brh, and its film thickness is th, a longitudinal biasing ratio defined by Brhxc2x7th/BS2xc2x7t2 is below 4.
A nonmagnetic layer is interposed between the second ferromagnetic layer and the second antiferromagnetic layer.
The first antiferromagnetic layer is made of an ordered alloy antiferromagnetic film expressed by Mnxe2x88x92M1 in which M1 is composed of at least one or more elements of Ni, Ru, Rh, Pd, Ir and Pt, and the second antiferromagnetic layer is made of a disordered alloy antiferromagnetic film expressed by Mnxe2x88x92M2 in which M2 is composed of at least one or more elements of Cr, Fe, Ru, Rh, Pd, Ir and Pt.
Further, in the present invention, a method for fabricating a magnetoresistive head including depositing a first and a second ferromagnetic layers via a nonmagnetic conductive layer or a nonmagnetic tunneling barrier layer; providing a first antiferromagnetic layer opposite to the nonmagnetic conductive layer or the nonmagnetic tunneling barrier layer to form a magnetoresistive film; forming a pair of electrodes for flowing a sense current to the magnetoresistive film; arranging a second antiferromagnetic layer so as to provide unidirectional magnetic anisotropy to the second ferromagnetic layer; arranging a hard magnetic film so as to apply a magnetic field to the second ferromagnetic layer; arranging a magnetic flux guide for guiding an external magnetic field to the second antiferromagnetic layer; and arranging a third antiferromagnetic layer so as to provide unidirectional magnetic anisotropy to the magnetic flux guide, includes a process for finally deciding by the direction of a magnetic field applied at annealing the direction of unidirectional magnetic anisotropy provided to the first ferromagnetic layer by the first antiferromagnetic layer and the direction of unidirectional magnetic anisotropy provided to the second ferromagnetic layer or the magnetic flux guide by the second antiferromagnetic layer, wherein the process subjects the first antiferromagnetic layer, the second antiferromagnetic layer or the third antiferromagnetic layer to annealing in the magnetic field under conditions of a temperature set from high to low in order of decreasing blocking temperature so as to provide the unidirectional magnetic anisotropy.